1. Field of the Invention
The present invention relates to methods of enhancing the growing process of vegetables, preferably living vegetables, most preferably living plants and/or seeds, and in general the invention is applicable to several fields of plant growing such as extensive and intensive agriculture, biotechnology, forest engineering, horticulture and gardening. The invention involves the use of nitric oxide (NO) to improve, enhance and/or increase the crop performance during any of the stages in the crop culturing, including sowing, growth and development, flowering and fruit formation or during any process associated with culture handling, such as transplantation, rooting, and other activity that could involve or lead to stress conditions for the plants and seeds.
To the purpose of the present specification, all the times that reference is made to the application of the invention to plants it is meant that the invention is broadly and generically applied to vegetables and plants in their broadest definition, including vegetables, plants,stem cutting, plantlets and seeds, preferably in a living state.
2. Description of the Prior Art
It is well known that the nitric oxide (NO) is an endogenous free radical formed in a variety of cell types by NO-synthase. Several roles and applications have been described for NO in animals (Hibb et al., Biochem. Biophys. Res. Commun., 157: 87-94, 1988; Ignarro et al., Annu. Rev. Pharmacol. Toxicol. 30: 535-560, 1990 and Snyder, S. H. Science 257: 494, 1992).
Evidence has been reported to demonstrate that NO may also be part of the functional complexity in the plant kingdom, thus, some publications and works have been referred to this matter such as the accumulation of potato phytoalexins by application of a NO-releasing compound (Noritake et al., Plant Cell Physil. 37: 113-116, 1996); the presence of NO/cyclic guanylyl monophosphate (cGMP)-sensitive transduction pathway in potato (Pfeiffer et al., J. Endothelial Cell Res. Vol. 3, Abstract 66, 1995); and western blot analysis revealed positive immunoreactivity with rabbit anti-brain Nitric Oxide Synthase (NOS) antibodies in pea embryonic axes and wheat germ (Sen et al., Biochem. Arch. 11: 221-227, 1995).
In senescing pea foliage NO emission was promoted by the addition of an ethylene precursor whereas in rapidly growing pea foliage three NO-releasing compounds inhibited expansion, this being suggested as a new pathway in the regulation of plant growth (Leshem et al., J. Plant Physiol. 148: 258-263, 1996).
The WO 99/15022 discloses a method for reducing the rate of deterioration of perishable horticultural produce by the use of NO. This method is applicable in fruit, vegetables and/or flowers during post-harvest handling, storage and marketing. This WO Document remarks that the application of nitric oxide at low concentrations has been found to reduce the production of ethylene by young, growing vegetative cells from epidermis and foliar cells.
Both toxic and protective activities for NO have been demonstrated in different cellular systems. Toxic effects have been predominantly observed at high NO concentrations, in human immunological system for example, where a high NO production also has been described (Filep et al., Blood 87: 5136-5143, 1997). On the other side, in systems where toxicity comes mainly from the generation of other free radicals, like reactive oxygen species, NO can provide protection against cellular damage. This is accomplished by NO ability to scavenge ROS and, therefore, end chain-propagate reactions (Wink et el., Proc. Natl. Acad. Sci. USA 90: 9813-9817, 1993). NO reduced cell death produced in several systems, especially when mediated by the Fenton reaction (Sergent et al., Hepathology 25: 122-127, 1997 and Yoshie et el., Arch. Biochem. Biophys. 342: 13-21, 1997). Moreover, NO preserves the level of chlorophyll and diminishes cell death in potato leaves infected by Phytophthora infestans (Laxalt et al., Europa J. Plant Pathol. 103: 643-651, 1997).
It would be therefore convenient to have a method, based in the application of nitric oxide, for enhancing the metabolic functions and growing process of plants and seeds that result in better developments and productions of plants, in the agricultural field, for example.